function element(list, index) {
  return list[index]
}

function is_in(list, obj) {
  return list.indexOf(obj) != -1
}

function is_not_in(list, obj) {
  return !is_in(list, obj)
}

function has_duplicate(list) {
  return new Set(list).size != list.length
}

Object.assign(exports, 
              { element,
                is_in, 
                is_not_in, 
                has_duplicate, })